Currently, power amplification methods comprise power transistors that have to be biased, using a bias voltage, so that the power transistors may amplify the radiofrequency signal to be transmitted to a base station, for example. Generally, the bias voltage of power transistors may be controlled adaptively using switched-mode power supplies, but these switched-mode power supplies are difficult to integrate, notably in cellular mobile telephones, and they have the drawbacks of causing power losses when the power transistors are operating.
Moreover, the radiofrequency signal intended for amplification may include an envelope signal which is not constant. Such is the case with the Wideband Code Division Multiple Access (W-CDMA) standard, which is used in third generation radio communication. When the radiofrequency signal includes a modulated envelope signal, the linearity and efficiency of the power transistors are reduced.
For conventional power transistors, for example, class A, the transistor bias voltage may be chosen to be very low in order to increase the efficiency of the transistor. However, by choosing a bias voltage that is too low, the distortion, in other words the spurious harmonics, in and around the amplified signal is increased.